Interchangeability of halogen and ethynyl substituents in the solid state structures of di- and tri-substituted benzenes

Examination of the solid state structures of bromo- and fluoro-substituted ethynylbenzenes, determined by single crystal X-ray diffraction, has demonstrated that the halogen and ethynyl substituents on these 1,4- and 1,3,5-substituted benzene rings can be interchanged without significant changes in their average solid state structures. Consideration of these structures, together with those of 1,4- and 1,3,5-substituted halogenobenzenes, suggests that, in most cases, shape complementarity may be of equal importance to interactional complementarity when attempting to rationalise the packing of these molecules in the solid state.